Endocrine and Nervous System Flashcards
The two parts of the nervous system
Central Nervous System
- Brain and spinal cord
- Control centre
Peripheral Nervous System
- Nerve cells, receptors
- Carry messages to and from CNS
Functional Types of Neurons
- Sensory
- carry messages from receptors in sense organs towards CNS - Motor
- Carry messages away from CNS - Interneuron
- Link between sensory and motor neurones in the CNS
Structural types of Neurons
- Multipolar
- Bipolar
- Unipolar
- Pesudounipolar
Conduction along myelinated fibres
In unmyelinated fibres, depolarisation of one area of the membrane causes another repolarization immediately next to the original stimulus
This process repeats along the whole membrane, moving away from the original stimulus, from one channel to the next
The nerve impulse is prevented from going backwards by the refractory period
Conduction along myelinated fibres
In myelinated fibres, the nerve fibres are insulated from the extracellular fluid by schwann cells
Ions cannot flow where the fibre is insulated so no action potential can occur, except at the nodes of ranvier
Sodium ions will diffuse along axon through the cytoplasm until they reach the next exposed gate (node of ranvier), the action potentials are said to jump from one node to another
With action potentials only occurring at the nodes of ranvier, there is less distance to cover = much faster
Conduction along a myelinated axon is also called saltatory conduction
Synapses
- Nerve impulse reaches axon terminal which activates voltage-gated ion channels in presynaptic membrane
- Calcium ions flow into the presynaptic axon terminal
- This stimulates the release of chemicals called neurotransmitters from vesicles by exocytosis at the presynaptic membrane
- The neurotransmitters diffuse across the synaptic cleft and attach to receptors on the postsynaptic membrane
- This stimulates ligand-gated protein channels to open, which allows an influx of sodium ions into the dendrite, initiating a nerve impulse in the next neuron
Examples of Neurotransmitters
→ Acetylcholine → Noradrenaline → Dopamine → Histamine → Serotonin
Removal of Neurotransmitters
Diffusion
→ Neurotransmitters exit the synaptic cleft via diffusion as they move from a high to a lower concentration
Enzymes degradation
→ Enzymes can inactivate the neurotransmitter, these are released by the postsynaptic membrane when the neurotransmitter has been received
Active reabsorption
→ Reabsorbed back into the presynaptic axon terminal by active transport
In the intracellular and extracellular fluids the concentrations are:
→ Extracellular fluid has a high concentration of sodium ions and chlorine ions
→ Intracellular fluid has a high concentration of potassium ions and various negative ions and low concentrations of sodium and chlorine ions
The cell membrane is:
Highly permeable to potassium ions
Slightly permeable to sodium ions
Impermeable to large negative ions
→ Therefore there is a tendency for potassium ions to diffuse out of the cell, this makes the cell more negatively charged as its losing positive ions
The potential difference created is called the membrane potential
The resting membrane potential is the membrane potential/difference of unstimulated nerve cells
> -70 mV (millivolts) - This means the potential of the inside of the membrane is 70mV less than that of outside
Maintaining the potential difference in two ways
- Sodium potassium pump
→ Cell activity moves sodium ions out of the cell and potassium ions into the cell using sodium and potassium protein pumps, for every 3 sodium ion molecules released, 2 potassium ion molecules will be brought back - Cell membrane is not equally permeable to all ions which means many negatively charged ions are trapped inside the cell
Action Potential
When a sufficiently strong stimulus is applied to a nerve fibre, the membrane will become more permeable to sodium ions therefore sodium channels will open and diffuse into cell
→ This enables cell to be more positive inside than the outside and increases the potential difference
If the level of stimulation exceeds 15mV (-70 to -55) it is known as an All or None response and can be passed along axon
→ When it exceeds 15mV it is classified as a sufficiently strong stimulus
→ Doesn’t matter size of impulse, if above 15 it will go if it doesn’t nothing will happen
→ ‘passed along axon’ is known as the action potential
The movement of sodium ions is independent to the strength of the stimulus
The flood of sodium ions into the cell causes the inside of the cell to reach a charge of 0 and slightly positive → Depolarisation/switching of charges
To re-polarize the cell, the sodium channels close and potassium ions diffuse out of cell therefore potassium ions open to return and create a negative charge
When potassium channels remain open for longer what is needed the potential drops lower than the resting → hyperpolarized
The rapid depolarisation and repolarisation is called the action potential
The movement of an action potential along a nerve is known as the nerve impulse
Nervous system divides into two divisions
Central nervous system
Peripheral nervous system
Central nervous sytem
Brain and spinal cord
Peripheral nervous system
Nerves, receptors and effectors
Peripheral nervous system divides into two divisions
Afferent: carries into to CNS from receptors
Efferent: carries info away from CNS to effectors
Afferent division
- Somatic: carry info from receptors in skin, muscles or joints
- Visceral: Carry info from receptors in internal organs
Efferent division
- Somatic: carry info to skeletal muscles
2. Autonomic: Carry info to involuntary muscles and glands
Autonomic divisions
Parasympathetic: rest and digest
Sympathetic: fight or flight
What is a receptor
Detects changes in the body’s internal or external environment
Thermoreceptors purpose
Detect temperatures
Thermoreceptors location
Skin - detect external temp
Hypothalamus - detect internal temp
Thermoreceptors function
Hypothalamus collects information which can regulated body temperature
Osmoreceptors purpose
Detect osmotic pressure
